Corrosion inhibition of dimethyl sulfoxide



United Sims. ate

- CORROSION INHIBITION OF DlME'l-HYL SULFOXIDE. Vincent A. Sullivan, In,and Tor Halfdan Smedslund,

Chicago, lll., assignors' to The Stephan Chemical Company, Chicago, Ill,a corporation of Illinois No Drawing. Original application Jan. 4, 1954,Ser. No. 402,154. Divided and: this application Dec. 6, F Ser. No.707,073

' 7 claims. (Cl. 252-75 The invention relates to corrosion inhibition,and more particularly, to corrosion inhibition with respect to certainaqueous and anhydrous dimethyl sulfoxide compositions' which normallycorrode metals. 7

Dimethyl sulfoxide, which has the following formula:

had, heretofore, been considered little more than a laboratorycuriosity; but recently a number of particularly valuable uses have beendiscovered for dimethyl sulfoxide' in its" anhydrous form as well as inthe form of aqueous solutions thereof. Such uses include uses in brakefluids as well as in anti-freeze (aqueous) compositions. It has alsobeen found that dimethyl sulfoxide has a noticeable tendency to corrodemetals (only in the presence of air), particularly iron and steel, andthis tendency toward corrosion would ordinarily greatly limit the usesfor dimethyl sulfoxide.

The instant invention is based upon certain discoveries which have beenmade relating to corrosion inhibition of dimethyl sulfoxide compositons.Primarily these discoveries relate to the finding of certain ingredientswhich may act as corrosion inhibitors in a dimethyl sulfoxidecomposition; but also these discoveries relate to certain conditions towhich dimethyl sulfoxide compositions may be subjected so as to reducetheir tendency toward corrosion of metals.

It is, therefore, an important object of the instant in vention toprovide improved corrosion inhibition for dimethyl sulfoxidecompositions.

It is another object of the instant invention to provide aqueous andanhydrous dimethyl sulfoxide compositions which have improved corrosioninhibitors therein.

A further object of the instant invention is to provide a process ofdecreasing the corrosion of iron by dimethyl sulfoxide by maintaining anoxygen free atmosphere over the dimethyl sulfoxide and by dissolving acompatible inert base therein.

Yet another object is to provide dimethyl sulfoxide having dissolvedtherein in a concentration of 0.01-0.05 mol per liter a compatiblenon-corrosive base.

Other objects, features and advantages of the invention will becomeapparent to those skilled in the art from the following detaileddisclosure of specific examples of preferred embodiments of theinvention.

The invention consists in a composition consisting essentially ofaqueous or anhydrous dimethyl sulfoxide and, as a corrosion inhibitor, acompatible inert base dissolved therein in a concentration of about0.005-01 mol per liter. In the aqeous dimethyl sulfoxide composition thebase imparts a pH of about 8-12, and preferably about 9-11, to thecomposition. The base used in the anhydrous dimethyl sulfoxide also hasthis property (with respect to aqueous dimethyl sulfoxide) but the pHdetermination in anhydrous dimethyl sulfoxide is not as clear cut adetermination.

2,948,683 Patented Aug. 9, 1960 Dimethyl sulfoxide is somewhathygroscopic and, therefore, anhydrous dimethyl sulfoxide or CF. dimethylsulfoxide usually has small amounts of water up to 0.1% which may bepicked up by the dimethyl sulfoxide whenever it is exposed to moist air.As used herein, anhydrous dimethyl sulfoxide is C.P. dimethyl sulfoxidewhich contains not more than 0.1 weight percent moisture and has amelting point of at least 18.4 C. Aqueous dimethyl sulfoxide thus is adimethyl sulfoxide composition containing at leastmorethan the moisturecontent for CF. dimethyl sulfoxide and, for practical purposes at leastabout 10 weight percent-of water. For practical purposes also theminimumamount of dimethyl snlfoxide in water is about 10 weight percent (or a10% aqueous dimethyl sulfoxide solution). 1 Preferably, a 30-60% aqueousdimethyl sulfoxide solution is used, since such a solution has asufficiently depressed freezing point to make it particularly valuablefor a number of uses including that of an anti-freeze composition. A 45%aqueous dimethyl sulfoxide solution is particularly useful, having afreezing point of minus 25 F.

The bases which may be used in the practice of the instant invention arepreferably soluble in dimethyl sulfoxicle and/ or water and mostpreferably both. At least, such bases are soluble in the medium usedwhich is either anhydrous or aqueous dimethyl sulfoxide; and the base iscapable of imparting a pH of at least about 8-12, and preferably about9-11, to the aqueous dimethyl sulfoxide using the proportions of basehereinbefore set forth.

The inorganic bases which may be used are preferably salts of a strongbase (i.e NaOH, KOH and NI-I OH) with a weak acid such as nitrous,phosphoric, chromic, boric, carbonic, etc. Typical examples of preferredinorganic bases are sodium nitrite, potassium nitrite, potassiumchromate, tn'sodium phosphate, sodium borate, sodium carbonate, andammonium hydroxide. Also, alkaline earth metal salts such as calcium andbarium nitrites are sufiiciently basic to be useful in the instantinvention. The nitrite in particular may be a salt of an alkaline earthmetal or an alkali metal.

Typical demonstrations of the corrosion inhibiting effect obtained inthe instant invention are shown in the following examples.

Example I A steel strip is immersed in C1. dimethyl sulfoxide (as acontrol) maintained at C. for six days and the strip is found to have abrass-like covering indicating a noticeable amount of corrosive action.If the process is repeated using a 45% aqueous dimethyl sulfoxidesolution (as a control) a black coating indicating more extensivecorrosive action is found on the strip.

A steel strip is immersed in a 45 aqueous dimethyl sulfoxide bath whichhas dissolved therein trisodium phosphate in a concentration of 0.005mol per liter so as to impart a pH of 12.3 thereto; and it is noted thatthe strip is substantially unchanged after being immersed in the bath at80 C. for 13 days.

Example II Using a bath of 45% aqueous dimethyl sulfoxide solutionhaving ammonium hydroxide dissolved therein in a concentration of 0.05imparting a pH of 11.8 thereto and maintained at 80 C., it is found thatthe steel strip retained therein for a period of 11 days issubstantially unchanged.

Example III A steel strip is immersed in 45 aqueous dimethyl sulfoxidesolution which has dissolved therein potassium nitrite in aconcentration of 0.01 mol per liter so as to impart a pH of 9.4 thereto;and the strip is maintained I inhibiting eformulation. I

tained if small amounts '(i.e., 0. 1:-2 Weight percent) of wettingagents such as sodium lauryl sulfate are included.

3 in a bath maintained at 180 C. for .11 days at which time it is foundthat the strip is. substantially unchanged.

' Example IV A procedure is carried out thatis the same as thatdescribed in the foregoing example except that potassium chromate issubstituted for potassium nitrite and the pH obtained is 10.6, and it isfound that the resultsobtained are substantially the same.

Other formulationswhich have been found to be particularly efiectiveinclude the following: I

. Formulations (45% aqueous dimethyl sulfoxide):

In addition, a particularly improvedcorrosioninhibit-i ing effect isobtained, if the bath is maintained in an oxygen free atmosphere (suchas acetylene). I Acetylene is preferred for this purpose because it issoluble. in- .dimethyl sulfoxide; but any oxygen free (i.e. gas freefrom molecularoxygen) gas maybe used, such as nitrogen,

ammonia, etc. The effectiveness of the step of excluding oxygen from thezone in which the strip is immersed 'in'the dimethyl sulfoxide bath isparticularly noticeable if a portion of the strip is positionedatthebath liquid level.

- I i It will be noted that an improvement in the corrosion inhibitingeffect is obtained if small amounts. (Ii. e.',, 1 .5 1

weight percent) of kerosene are included in the corrosion Also, animprovement 15 b- Potassium nitrite appears to be the most effectiveinorganic base. :This is a division of our'application Serial No.402,154, filed January 4, 1954.

' Said application Serial No. 402,154 has now issued as US. Patent No.2,818,388.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention.

We claim as our invention:

1. A composition consisting essentially of aqueous dimethyl sulfoxideand, as a corrosion inhibitor, a soluble inert inorganic salt of astrong base and a weak acid dissolvedthereinin a. concentration of0.0050.1 mol per liter and imparting a pH of 812 to the composition.

2. A composition consisting essentially of aqueous-dimethyl sulfoxideand, as a corrosion inhibitor, a soluble inert inorganic saltof analkali metal base and. a weak acid dissolved therein in a concentrationof 0.005-01 mol per liter andimparting a pH of 8-12 to the composition.

3. A composition consisting essentially of. aqueous 1 dimethyl sulfoxideand, as a corrosioninhibitor, a soluble inert base dissolved thereinselected from the class consisting of alkali metal salts of nitrous,phosphoric;

chromic, boric and carbonic acids dissolved therein in a concentrationof 0.005-0.1-mol.per liter and imparting a pH of 8-12 to thecomposition. I I 4. A composition consisting essentially of aqueous.dime'thyl' sulfoxide and, .as a. corrosion inhibitor, an alkali metalnitrite dissolved therein in a concentration of 0.0050.1 13101 per literand imparting a pH of 812 to the composition.

5. Dimethyl sulfoxide having dissolved therein in a concentration of0.01-0.05 mol per liter a compatible non corrosive inorganic saltof astrong base and a weak acid.

6. Dimethyl sulfoxide having dissolved therein ina concentration of0.0.1-0.05 mol. per liter a compatible non-corrosive alkali metalnitrite. I

7. A process of decreasing the corrosion of ironby I dimethylisulfoxidewhich comprises contacting iron with dimethyl-sulfoxide havingdissolved'therein 'a. compatible inert inorganic salt of a strong baseand a weak acid in an oxygen free atmosphere, said salt being present inthe dimethyl sulfoxide in a concentration of 0.01-0.05 moi. Y

per liter.

- .References Cited in the file ofthis patent UNITED STATES PATENTS2,602,779 Moyer July 8, 1952

1. A COMPOSITION CONSISTING ESSENTIALLY OF AQUEOUS DIMETHYL SULFOXIDE AND, AS A CORROSION INHIBITOR, A SOLUBLE INERT INORGANIC SALT OF A STRONG BASE AND A WEEK ACID DISSOLVED THEREIN IN A CONCENTRATION OF 0.005-0.1 MOL PER LITER AND IMPARTING A PH OF 8-12 TO THE COMPOSITION. 